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clinuxsystem

Can't set file with "echo" from a program via system()

I'm try to use system("echo 1 > /sys/class/afile") to set a file to 1.

If I use it on console it works well, but if I run my C program it shows me:

sh: echo: I/O error

I already try to set it with following code:

char i[1];
i[0]=1;
int fd1 = open("/sys/class/afile",O_CREAT | O_WRONLY);
int ret = write(fd1,i,strlen(i));
if(ret > 0)
   printf("Ok\n");
else
   printf("nOk\n");
close(fd1);

The result is "Ok" but the file didn't change.

Solution

  • strlen(i) yields undefined behavior because i is not a string; the array lacks room for null termination. Also, i[0]=1; does not put a '1' character in the array, but rather puts a byte with value 1, which is a "^A character".

    Instead try write(fd, "1", 1) - no need for any variables or strlen.